Abstract

The carbon balance of terrestrial ecosystems is particularly sensitive to climatic changes in autumn and spring(1-4), with spring and autumn temperatures over northern latitudes having risen by about 1.1 degrees C and 0.8 degrees C, respectively, over the past two decades(5). A simultaneous greening trend has also been observed, characterized by a longer growing season and greater photosynthetic activity(6,7). These observations have led to speculation that spring and autumn warming could enhance carbon sequestration and extend the period of net carbon uptake in the future(8). Here we analyse interannual variations in atmospheric carbon dioxide concentration data and ecosystem carbon dioxide fluxes. We find that atmospheric records from the past 20 years show a trend towards an earlier autumn- to- winter carbon dioxide build- up, suggesting a shorter net carbon uptake period. This trend cannot be explained by changes in atmospheric transport alone and, together with the ecosystem flux data, suggest increasing carbon losses in autumn. We use a process- based terrestrial biosphere model and satellite vegetation greenness index observations to investigate further the observed seasonal response of northern ecosystems to autumnal warming. We find that both photosynthesis and respiration increase during autumn warming, but the increase in respiration is greater. In contrast, warming increases photosynthesis more than respiration in spring. Our simulations and observations indicate that northern terrestrial ecosystems may currently lose carbon dioxide in response to autumn warming, with a sensitivity of about 0.2 PgC degrees C-1, offsetting 90% of the increased carbon dioxide uptake during spring. If future autumn warming occurs at a faster rate than in spring, the ability of northern ecosystems to sequester carbon may be diminished earlier than previously suggested(9,10).

Published in

Nature
2008, Volume: 451, number: 7174, pages: 49-53
Publisher: NATURE PUBLISHING GROUP

SLU Authors

• Grelle, Achim

  • Department of Ecology, Swedish University of Agricultural Sciences
    

Sustainable Development Goals

SDG15 Protect, restore and promote sustainable use of terrestrial ecosystems, sustainably manage forests, combat desertification, and halt and reverse land degradation and halt biodiversity loss


UKÄ Subject classification

Renewable Bioenergy Research
Environmental Sciences related to Agriculture and Land-use
Forest Science


Publication identifier

DOI: https://doi.org/10.1038/nature06444

Permanent link to this page (URI)

https://res.slu.se/id/publ/24067